1. Field of the Invention
The present invention relates to an interdigitated electrode for an electronic device and an electronic device using the same, and more specifically, to an interdigitated electrode for an electronic device which has a symmetric structure, such as a circular structure or a polygonal structure, and an electronic device using the same.
The present invention has been produced from the work supported by the IT R&D program of MIC (Ministry of Information and Communication)/IITA (Institute for Information Technology Advancement) [2006-S006-01, Components/Module technology for Ubiquitous Terminals] in Korea.
2. Discussion of Related Art
In general, an electronic device includes a sensor, an actuator, and a micro-electro-mechanical system (MEMS) device. The sensor functions to detect and measure various physical quantities. Some types of sensors are a piezoelectric sensor formed of a piezoelectric material, an acoustic sensor, a piezoelectric acoustic sensor, and a pressure sensor. The actuator performs mechanical functions using energy and may be, for example, a piezoelectric actuator. The MEMS device is used for microelectronic systems and may include a MEMS acoustic sensor, a MEMS actuator, or a MEMS speaker. The electronic device may include an electrode used for converting capacitance or energy.
Hereinafter, an electrode for a conventional electronic device will be described with reference to FIG. 1.
FIG. 1 is a cross-sectional view of a conventional electronic device. Conventionally, an electronic device 1 includes upper and lower electrodes 14 and 12 located on and under a piezoelectric layer (PZT) 13, respectively. An oxide layer 11, the lower electrode 12, the PZT 13, the upper electrode 14, and an oxide layer 15 are disposed on a substrate 10. A metal 16 is connected to an end portion of each of the lower and upper electrodes 12 and 14. In the electronic device, the substrate 11 is formed of bulk silicon (Si), and the oxide layers 11 and 15 are formed of silicon oxide (SiO2), silicon nitride, or zinc oxide. The lower and upper electrodes 12 and 14 are formed of titanium/platinum (Ti/Pt), aluminum (Al), Pt, tungsten (W), or tantalum (Ta). In the electronic device 1 shown in FIG. 1, the metal 16 is formed of Al.
However, in the case of the foregoing electronic device 1, since the upper and lower electrodes 14 and 12 should be provided on and under the PZT 13, the fabrication process becomes complicated. In particular, the flow of electricity makes an angle of 90° with an electrode direction in a sensor or actuator using the PZT 13, so that the sensor or actuator has a far smaller piezoelectric coefficient. Thus, the structure of the electronic device 1 may deteriorate the sensitivity of the sensor or the efficiency of the actuator.
In order to solve this problem, a technique using an interdigitated electrode (IDE) has been proposed. FIG. 2 is a plan view of an IDE used for a conventional electronic device. For simplicity, other components of a MEMS device besides the IDE will not be described.
Referring to FIG. 2, an IDE 20 is a linear IDE in which an anode 21 and a cathode 22 are repetitively interdigitated. As is known, the linear IDE 20 may be used for some MEMS devices, such as a cantilever sensor or a cantilever actuator. Thus, the linear IDE 20 may drive a cantilever or generate a voltage in a pressure-deformed cantilever and apply the voltage to the cantilever sensor. The foregoing linear IDE 20 may be employed in various electronic devices. For example, the linear IDE 20 may be used for a comb driver or a planar acoustic sensor. Alternatively, the linear IDE 20 may be used for a sensor or an actuator of a linear piezoelectric structure so that the surface of an electrode is elevated to increase sensitivity or drivability. In another case, the linear IDE 20 may be used for a biological sensor or a gas sensor to increase an electrode contact area. Since both the anode 21 and the cathode 22 are located on one surface of the linear IDE 20, it is easy to manufacture the linear IDE 20.
The linear IDE 20 is adequate for linear and comb-type devices, such as a square device or a cantilever device. However, it is difficult to install the linear IDE 20 on a symmetrical structure, for example, symmetric oscillation and actuation plates. When installed on such symmetrical structures, the efficiency of the linear IDE 20 decreases.